If you are going to use those Mitu objectives on a camera with tube lens, then you are very unlikely going to use that 100x objective. Very few forum members here ever used such high magnification for hobbyist photography. None uses 100x routinely, I would think.

With 100x on sensor magnification, your subject of interest would be around 0.2mm in size and very thin/light. That makes it difficult to handle or prepared for viewing/photography.

A much more useful magnification in the Mitu product line is 7.5x or 5x.

Below 4x, your MPE is good enough.

If you are viewing biological subjects with cover slip and biological objectives, then you may use 100x immersion objective quite often._________________Selling my Canon FD 200mm F/2.8 lens

I agree.
Also the 10x NA 0.28 is a great objective - oneof the most useful.
The 100x you have is a "SL" which means that the NA is only 0.55, the same as a regular 50x, and with the same 13mm working distance. Therefore a 50x would resolve (almost) the same and have 4x the coverage.

Untested, they're both a heck of a risk. A high proportion is substandard and practically unsaleable, due to invisible bad handling.
I'd ask for further couple of weeks to test, and if he refuses, return them._________________Chris R

I agree with most of what Fan and ChrisR have said already, but will repeat some of it more emphatically: I think you should probably return the 20x, and certainly return the 100x.

Other than myself, I don’t know of anyone who routinely tests Mitutoyo objectives. Unfortunately, I can’t handle these for you because of their BD threads. My rig is set up for the M26 (26mm x 36 tpi) threads found on standard Mitutoyo M Plan objectives, not the larger 40mm x 36TPI threads on Mitutoyo BD objectives. (You’ll note that BD objectives typically sell for less than their M26 counterparts; I’m sure this is largely due to their less common threading.)

Even if you obtained a return-period extension and received your Rafamera adapter in time, you are not in a position to test these objectives yourself. First, one must have a known-good lens to test against in direct comparison. When I test Mitutoyo objectives, I’m comparing an unproven objective with one of my known-good objectives. Without a known-good 20x in hand, you don’t have a benchmark.

Also, there is a sizeable learning curve in moving up from your 1-5x MP-E 60mm to a 20x objective. It’s not unlikely that you’ll run into issues with vibration, lighting, subject positioning, and other things. While you will work through these things with time and practice, a lens-test under time pressure is not a good first project at higher magnifications.

Regarding the SL 100x objective, the SL series of Mitutoyo objectives is not very good for macro work. The modest numerical apertures of these lenses limit their resolution. The SL 100x/0.55, in particular, strikes me as a particularly unfortunate beast, with the lower resolution typical of a 50x, and the more-difficult handling of a 100x. I would suggest returning that objective without even considering a test.

zzffnn wrote:

If you are going to use those Mitu objectives on a camera with tube lens, then you are very unlikely going to use that 100x objective. Very few forum members here ever used such high magnification for hobbyist photography. None uses 100x routinely, I would think.

As a counterexample, I routinely use a Mitutoyo 100x/0.70 on my macro rig, and do not think this magnification out of reach for macro photographers. This said, I mostly agree with Fan in spirit. 100x on a macro rig requires rock solid equipment and work flow. If you’re just now moving up from 5x, and waiting for an adapter to put on your 200mm lens, your setup will probably not work well at 100x. 100x can be done by most of us, but perhaps only after some time and money are spent to accommodate it.

zzffnn wrote:

With 100x on sensor magnification, your subject of interest would be around 0.2mm in size and very thin/light. That makes it difficult to handle or prepared for viewing/photography.

Often, the subject is larger, but some detail of interest is this small. But Fan’s point is solid. I can only work at 100x by using micrometers to position the subject. This said, micrometer positioning is very useful even at low magnifications, such as 4x. I’ve wondered how anyone works without it?